May 13, 2005

Coastal migration theory

Two new papers in the new issue of Science are in support of the coastal Out of Africa migration hypothesis. According to this theory, the earliest Out of Africa members of our species followed the coastline of Asia, eventually reaching Australia, rather than heading towards the interior of the Eurasian landmass.

In Single, Rapid Coastal Settlement of Asia Revealed by Analysis of Complete Mitochondrial Genomes, Vincent Macaulay and colleagues sampled mitochondrial DNA from the Orang Asli of Malaysia. They found that these peoples possess a certain degree of admixture from other Southeast Asians, which was introduced in Holocene and subsequent periods, but they mostly have their own highly-specific, and very old subclades of macrohaplogroups N, M, and R. These macrohaplogroups, taken together, account for almost all non-African mtDNA. So, apparently the ancestors of all non-Africans were apparently involved in the very early migration Out of Africa from which the aboriginal Malaysians and also the Australasians are descended, and there was not a separate "northern" and "southern" migration Out of Africa.

In Reconstructing the Origin of Andaman Islanders, Kumarasamy Thangaraj and his colleagues studied the mtDNA of Andaman and Nicobar islanders. The former are Negritos physically, while the latter are Mongoloid. The Andamanese belong only in Y-haplogroup D and mt-haplogroup M, and the authors attribute this to a founder effect, as they are a very small isolated population. In contrast, the Nicobarese seem to descend from southeast Asians in more recent times, as their mtDNA sequences match those of people from China, Malaysia and Thailand.

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